1. Field of the Invention
The present invention relates to a biological-information obtaining apparatus, particularly to a biological-information obtaining apparatus capable of obtaining a pulse wave velocity (PWV) and a processing method thereof.
2. Description of the Related Art
The PWV represents the propagation velocity of a pulse wave propagating through arteries, and is known for its helpfulness in finding cardiovascular diseases such as arterial sclerosis. As a method of determining such a PWV, for example, use of an apparatus is known that determines two locations used in the detection of a cardiac-beat synchronizing signal in blood-vessel patterns and determines a PWV on the basis of the distance between the two locations and the time when the cardiac-beat synchronizing signal is generated.
As such an apparatus, for example, an apparatus with a phonocardiographic transducer to be attached onto the skin of the chest and a pressure sensor to be wound around the brachial region has been developed for determining a PWV. Regarding such an apparatus with a phonocardiographic transducer and pressure sensor, a method of determining the length of a blood vessel has been proposed (see, for example, Japanese Unexamined Patent Application Publication No. 2003-230543, FIG. 1). In this example of the related art, the speed at which an ultrasonic wave propagates in biomedical tissue is stored, and the length of the blood vessel is calculated by dividing an observed value of the ultrasonic wave output from the phonocardiographic transducer by the speed.